Hypophosphorous acid (H.sub.3 PO.sub.2) also known as phosphinic acid, is currently a staple article of commerce which is sold by various companies for purposes such as the manufacture of hypophosphite salts, as well as to prevent the discoloration of phosphate esters, in esterification catalysts, and for the manufacture of cooling water treatment chemicals. It is also sold for use in metal finishing procedures, as a reducing agent for electroless plating, and as a sealer for phosphated steel.
The manufacture of hypophosphorous acid, however, has generally been carried out by somewhat complex and expensive methods utilizing ion exchange procedures. In these procedures, for example, the sodium ion of sodium hypophosphite is exchanged for a hydrogen ion using an ion exchange resin therefor. These procedures result in hypophosphorous acid being a rather expensive commodity, generally at over $7.00 per pound.
By way of background, Liaukonis et al., Issled. Obl. Osazhdeniya Met. (1985), pp. 134-9 sets forth a detailed study of the anodic polarization of the Ni--P electrode in an acetate solution of hypophosphite as a function of the pH. Furthermore, in Makarov et al., Zasch. Met. 18(6) pp. 918-919 (1982) the rate dependence of hypophosphite anion oxidation and the evolution of hydrogen on titanium is investigated for sodium hypophosphite solutions. These authors thus describe the application of a current to titanium electrodes in contact with nickel hypophosphite solutions therein. In accordance with the disclosure of this article, a conventional electroless nickel bath is contained in a titanium tank and the article concerns the tendency of the bath to plate onto that tank. Furthermore, Sadikov et al., Zasch. Met., 19(2), pp. 314-317 (1983), sets forth yet another investigation of the behavior of titanium hypophosphite electrolyte solutions.
Electrodialysis is also a known process which has been utilized for various purposes, such as that of U.S. Pat. No. 5,264,097. In that patent an alkali salt-containing aqueous solution including salts and complexes of metal anions and cations is fed to the catholyte, and the metal cations are removed therefrom as insoluble hydroxides by controlling the pH therein. In this process, the anions are transported across an anion permeable membrane into the anolyte, where they are converted to acids or halogens.
It is therefore of considerable interest to develop a novel and more economical method for producing hypophosphorous acid for the various uses discussed above.